The identification of a large fraction of the genes on chromosome 21q by Investigators of this PPG has lead to a number of specific, compelling hypothesis about how trisomy of single genes, and also how trisomy of functionally related sets of genes from chromosome 21q may contribute to aspects of the Down syndrome phenotype. Now we can test these genes singly and in the context of the recently developed moused Ts65Dn model of Down syndrome: with these development it has become possible to test these gene by either "adding" or "subtracting" one or more of these genes from the complement of genes trisomic in Ts65Dn, and assaying for the enhancement or amelioration of Down syndrome-like phenotypes in mutant mice. The purpose of this Core is to coordinate and centralize the production of single gene transgenics and single gene knockout mutants. Our target genes will be those identified by Investigators of this PPG as strong candidates for involvement in the Down syndrome phenotype. Not only will it be more efficient to have one transgenic facility, it will also facilitate standardization of the genetic background and initial analyses of mutant phenotypes. We will produce 5 "over-expressing" transgenic lines per year. In the first years of the grant, these will include over expression of CBS (cystathione beta synthase), RED1 (an RNA editase), GAPBA ( a transcription factor), DS-CAM (a cell adhesion molecule), and CHD-1 (a novel protein expressed in brain). We will make 2 knockouts per year from the region trisomic in Ts65Dn. In the first year, these will include Glur5 (a glutamate receptor subunit) and Gart (a protein with three activities of de novo purine synthesis). The mice produced in this Core will be analyzed both by the collaborating Investigators of the PPG as well as by the Behavior Screening Core (Dr. Crnic). While our initial approach to "over-expression" transgenics is the standard oocyte injection protocol (Hogan et al, 1991) which we have used successfully for Gart and Rfc transgenics, we are cognizant of the artefacts frequently encountered with this approach, e.g. altered transcriptional patterns and insertion site mutations (e.g. Burgess et al, 1995; Perry, et al, 1995). Accordingly, we are investigating the use of the recently developed Cre/lox system (Sauer, 1994) to target single copies of the transgenes to specific sites in the mouse genome, known to be transcriptionally permissive and non-mutagenic (Lasko et al, 1996).